1. Field of the Invention
The present invention relates to a high-frequency circuit device such as a waveguide or a resonator having two parallel planar conductors, and the invention also relates to communication apparatus using the same.
2. Description of the Related Art
As transmission lines used in microwave bands and millimeter-wave bands, for example, there are known grounded coplanar lines, each of which has a ground electrode formed on the substantially the entire surface of a dielectric plate and a coplanar line formed on the other surface thereof, grounded slot lines, each of which has a ground electrode formed on a surface of a dielectric plate and a slot line formed on the other surface thereof, and planar dielectric lines having slots formed on both surfaces of a dielectric plate, the slots opposing each other through the thickness of the dielectric plate.
Since each of the above transmission lines has a structure including two parallel planar conductors, for example, when electromagnetic fields are disturbed at the inputs/outputs and bends of the transmission lines, a spurious mode wave such as the so-called parallel-plate mode, which is a parallel plane mode, is induced between the two parallel planar conductors, and the spurious mode wave thereby propagates between the planar conductors. As a result, between adjacent transmission lines, interference is caused by a leakage wave of the above spurious mode, thereby often leading to leakage of signals.
FIG. 19 illustrates an example of electromagnetic-field distributions of the main propagating mode of a grounded coplanar line and a parallel-plate mode associated with the main propagating mode. In FIG. 19, reference numeral 20 denotes a dielectric plate. On substantially the entire lower surface of the dielectric plate 20 is formed an electrode 21, and on the upper surface thereof are formed a strip conductor 19 and electrodes 22. In this case, the electrodes 21 and 22 are used as ground electrodes, and the grounded coplanar line is comprised of these electrodes 21 and 22, the dielectric plate 20, and the strip conductor 19. In such a grounded coplanar line, disturbances of the electromagnetic fields occur at edges of the line to induce electric fields vertically running through the electrodes 21 and 22 formed on the upper and lower surfaces of the dielectric plate 20. As a result, a parallel-plate mode electromagnetic field is generated as shown in FIG. 19. In this figure, the arrows indicated by solid lines shows electric field distributions, broken-line arrows show magnetic field distributions, and dash-double-dot-line arrows show current distributions.
In order to prevent such spurious mode wave propagation, conventionally, an electric wall is formed along each side of the transmission line, for example, by a plurality of through-holes which electrically connect the electrodes formed on the upper and lower surfaces of the dielectric plate. The through-holes are spaced apart by distances much shorter than the wavelength of the propagating mode.
When the electric walls mentioned above, are formed along the direction in which an electromagnetic wave of the transmission line propagates, the electric walls serve to block the propagation of a spurious mode wave such as a parallel plate mode wave. However, a problem with this arrangement is that the spurious mode wave is reflected by the electric walls back to the transmission line. Eventually, the spurious mode wave is likely to be converted into the mode of the transmission line.
Accordingly, it is an object of the present invention to provide a high-frequency circuit device and a communication apparatus using the same that can solve the above-described problems caused by the reflection of a spurious mode wave occurring at a location where the propagation of the spurious mode wave is blocked so as to block the propagation of a spurious mode such as a parallel plate mode.
For example, in the case of a grounded coplanar line, with disturbances of electromagnetic-fields generated by a strip conductor forming the grounded coplanar line and electrodes disposed at the sides thereof, the electromagnetic wave of a spurious mode such as a parallel plate mode propagates between two parallel conductors, and when the electromagnetic wave reaches the boundary of a conductor pattern, a part of the electromagnetic wave is reflected at the boundary of the conductor pattern. The present invention uses this reaction to suppress the spurious mode such as the parallel plate mode.
In other words, according to an aspect of the present invention, there is provided a high-frequency circuit device including at least two parallel planar conductors, an electromagnetic-wave excitation circuit exciting an electromagnetic wave between the two planar conductors, and a spurious-mode reflection circuit reflecting a spurious mode wave propagating between the two planar conductors. In this high-frequency circuit device, the spurious-mode reflection circuit is disposed apart from the electromagnetic-wave excitation circuit by a distance at which the electromagnetic-wave excitation circuit cancels the wave reflected by the spurious-mode reflection circuit. With this arrangement, the spurious mode wave propagating between the two parallel planar conductors is reflected by the spurious-mode reflection circuit, and then, the reflected wave is cancelled after returning to the electromagnetic-wave excitation circuit. The spurious-mode reflection circuit is formed by using the conductor pattern of each of the parallel planar conductors.
In addition, for example, the distance between the spurious-mode reflection circuit and the electromagnetic-wave excitation circuit, which is represented by the symbol w, may be obtained by the following equation:
xe2x80x83w={mxcfx80xe2x88x92arg(xcex93)}/[2k{1xe2x88x92(xcex2/k)2}]
In this equation, the symbol m represents an odd number of 1 or greater, the symbol arg(xcex93) represents a reflection phase in the reflection circuit, the symbol k represents a vector k with respect to a direction in which the spurious mode wave propagates, and the symbol xcex2 represents a phase constant of the main propagating mode of the electromagnetic-wave excitation circuit.
In addition, the spurious-mode reflection circuit may be comprised of a plurality of micro-strip lines disposed at distances from each other, the distances being shorter than the length of an electromagnetic wave.
In addition, the spurious-mode reflection circuit may be either a magnetic wall or an electric wall generated on a dielectric plate having the two planar conductors formed thereon.
In addition, the electromagnetic-wave excitation circuit may be a transmission line. For example, this arrangement can prevent interference of the spurious mode wave between adjacent transmission lines and interference of the spurious mode wave between the transmission line and a resonator.
In addition, the electromagnetic-wave excitation circuit may be a resonator. This arrangement can prevent, for example, interference of the spurious mode wave between adjacent resonators and interference of the spurious mode wave between the resonator and the transmission line.
Furthermore, according to another aspect of the present invention, there is provided a communication apparatus including the above-described high-frequency circuit device, which is used in a communication-signal propagating unit, wherein a signal processing unit such as a filter passes and/or blocks the communication signal in a specified frequency band.